Currently, the NCDOT is in the process of deconstructing the 56 year old Bonner Bridge. This deconstruction provides an opportunity to evaluate the aged girders of the bridge and to compare their performance to load rating calculations. Such a comparison will provide a better understanding of the accuracy and assumptions associated with prestressing losses and will allow for refinements to the load rating procedures. The bridge girders that have been in service for 56 years have undergone ageing and degradation from being exposed to the natural environment. Some of the girders have been damaged and repaired. Load testing these girders can help quantify the effects of degradation, damage, and repair to be able to provide a better understanding of the accuracy of current load rating assumptions.
This proposal focuses on a complete performance evaluation of the Bonner Bridge girders including full-scale load testing of 4-6 of the 61 ft. by 45 in. deep AASHTO Type III girders. The load testing will be conducted in the Constructed Facilities Lab (CFL) located at North Carolina State University. The proposal will also conduct an evaluation of the literature and best practices for calculating prestressed girder losses and for determining the capacity for both repaired and unrepaired (deteriorated) girders. The research will provide recommendations for updates to the NCDOT Structures Management's Manual guidelines. These assessments will also include directly evaluating the current amount of stress (after losses) in the girder prestressing steel; the condition, strength and stiffness of the concrete materials; and the location and extent of damage and repair of the girders.
To accomplish these objectives the following five tasks will be conducted:
- Literature review of relevant research including NCDOT policy and procedures
- Review of best practices for calculating prestressed girder losses and remaining capacity
- Investigation of Bonner Bridge history and corresponding assumptions made for load ratings
- Full-scale experimental testing of 4-6 Bonner Bridge girders
- Development of recommendations for NCDOT specific design and load rating policy
The research products that will result from these tasks includes:
- Summary of the performance of Bonner Bridge girders based on the full-scale tests of the 4-6 bridge girders in conjunction with materials data and strand cutting data.
- Summary of the condition of the existing girders with respect to materials performance, load rating performance and prestressing losses.
- Provide clear and practical recommendations for more accurate procedures for estimating prestressing losses and load rating performance.
- Provide clear and practical recommendations for load rating guidance corresponding with AASHTO LRFD and the MBE.
- Provide clear recommendations to changes that can be made to the Structure Management's Design Manual Guidelines and overall Structures Management Unit policies.